Heating apparatus for vaporizer

ABSTRACT

A vaporizer heating apparatus is comprised of electromagnetically responsive material and electrically non-conductive material. A antimicrobial fluid to be vaporized, such as water or hydrogen peroxide solution, is supplied to the heating apparatus where it is converted to a vapor. In one embodiment of the present invention, electromagnetically responsive material particulate is embedded into the electrically non-conductive material. In another embodiment of the present invention, a microwave generator is used to produce heat.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 10/167,910, filed Jun. 12, 2002, and is hereby fullyincorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to a vapor generator. Itfinds particular application in conjunction with steam and hydrogenperoxide vapor systems used in connection with medical devicedisinfection and sterilization and in the sanitation, disinfection, andsterilization of rooms, buildings, large enclosures, and bottling,packaging, and other production lines and will be described withparticular reference thereto. It should be appreciated, however, thatthe invention is also applicable to other chemical vaporization systemssuch as those employing other peroxides, peracids, and the like.

BACKGROUND OF THE INVENTION

[0003] A variety of microbial decontamination processes employsterilizing vapors, such as steam or a mixture of water vapor withanother antimicrobial (e.g., hydrogen peroxide vapor), in relativelylarge quantities. Steam sterilizers, for example, employ pressurizedhigh temperature dry steam as a sterilizing vapor. Dry steam ispreferred, as unvaporized water droplets can shield microbes or prionsfrom the steam. Hydrogen peroxide vapor systems use a flow of hydrogenperoxide vapor, typically at around atmospheric pressure or below.Again, the presence of water droplets is not beneficial, as they canshield microbes and prions from the peroxide vapor.

[0004] Medical, pharmaceutical, dental, and food packaging items areoften sterilized prior to use or reuse, in such systems. Vapors are alsoused in the decontamination of sterile enclosures and other clean roomsused by hospitals and laboratories. Processing equipment forpharmaceuticals and food, freeze driers, and meat processing equipmentare also advantageously disinfected or sterilized with a vapor.

[0005] In the case of steam, for example, microbial decontaminationsystems often create the steam by boiling water inside a reservoir of asteam generator, such as a boiler. A large heating element is usuallylocated over the bottom surface of the reservoir to maintain a supply ofboiling water.

[0006] In the case of other water-based antimicrobial vapors, such ashydrogen peroxide vapor, a vaporizer outside the chamber generates aflow of vapor. Typically, a solution of about 35% hydrogen peroxide inwater is injected into the vaporizer as fine droplets or a mist throughinjection nozzles. The droplets contact a heated surface which heats thedroplets to form the vapor, without breaking the hydrogen peroxide downto water and oxygen. A carrier gas is circulated over the heat transfersurface to absorb the peroxide vapor.

[0007] Such vapor generation methods have disadvantages when largequantities of vapor are desired or vapor is needed at short notice.Boilers tend to be relatively large pieces of equipment, which work bestwhen the wattage is spread out over a large heating element surfacearea. This keeps the watt density low and extends the life of theheating element. The large heating element surface area, however, takesup considerable space. Additionally, to avoid damage to the heatingelement, it is completely immersed in water. Thus, it takes some time toheat the large volume of water to steam temperature in order for steamgeneration to begin. It is expensive to maintain a supply of over 100°C. water ready for a demand. Any unused heated water generally has to becooled in a heat exchanger before it is disposed of in a municipal wastewater system.

[0008] Vaporized hydrogen peroxide is a particularly useful vaporsterilant for both vacuum sterilizing systems and rooms and other largeenclosures. It is effective at or close to room temperature, whichreduces the potential for thermal degradation of associated equipmentand items to be sterilized or disinfected within the sterilizerenclosure. In addition, hydrogen peroxide readily decomposes to waterand oxygen, thus simplifying disposal.

[0009] As the size of the sterilizer or enclosure increases, or thedemand for hydrogen peroxide is increased, the efficiency of thevaporization system becomes more significant. The capacity of thevaporizer is limited in a number of ways. First, the vaporizationprocess creates a pressure increase, reducing the flow of the carriergas through the vaporizer. Second, to maintain sterilization efficiency,the pressure at which the vapor is generated is limited to that at whichthe hydrogen peroxide is stable in the vapor state. Third, the timetaken to generate the hydrogen peroxide is dependent on the time takento heat a surface to the vaporization temperature of hydrogen peroxide.

[0010] One solution has been to increase the size of the vaporizer, theinjection rate of hydrogen peroxide into the vaporizer, and the flowrate of carrier gas. However, the carrier gas tends to cool the heatingsurface, disrupting the vaporization process. Heating the surface to ahigher temperature breaks down the hydrogen peroxide.

[0011] Yet another solution is to use multiple vaporizers to feed asingle enclosure. The vaporizers may each be controlled independently,to allow for variations in chamber characteristics. However, the use ofmultiple vaporizers adds to the cost of the system and requires carefulmonitoring to ensure that each vaporizer is performing with balancedefficiency. None of these solutions addresses the initial warm up timeneeded for raising the temperature of the vaporizer to the vaporizationtemperature.

[0012] The present invention provides new and improved vaporizationsystems and methods which overcome the above-referenced problems andothers.

SUMMARY OF THE INVENTION

[0013] In accordance with the present invention, there is provided avaporizer for vaporizing a fluid to form an antimicrobial vapor,comprising: (1) a source of electromagnetic radiation; and (2) a heatingapparatus for producing heat to vaporize an antimicrobial fluid passingtherethrough, including: (a) an electrically non-conductive material,and (b) an electromagnetically responsive material.

[0014] One advantage of the present invention is that a high output ofsterilant vapor is achieved.

[0015] Another advantage of the present invention is that it enablessterilant vapor to be generated “on demand” at short notice.

[0016] Another advantage resides in reduced resistive electrical powerloads.

[0017] Another advantage of the present invention is that it enablesvapor concentration levels to be raised rapidly, particularly when usedwith smaller enclosures, thereby reducing the conditioning time.

[0018] Still another advantage of the present invention is the provisionof a vaporizer constructed of materials that will not degradeantimicrobial fluids.

[0019] A still further another advantage of the present invention is theprovision of a vaporizer having reduced weight.

[0020] Yet another advantage of the present invention is the provisionof a vaporizer that is less costly to manufacture.

[0021] These and other advantages will become apparent from thefollowing description of preferred embodiments taken together with theaccompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention may take physical form in certain parts andarrangement of parts, a preferred embodiment of which will be describedin detail in the specification and illustrated in the accompanyingdrawings which form a part hereof, and wherein:

[0023] The invention may take form in various components andarrangements of components, and in various steps and arrangements ofsteps. The drawings are only for purposes of illustrating a preferredembodiment and are not to be construed as limiting the invention.

[0024]FIG. 1 is a schematic view of a first embodiment of a vaporizationsystem in accordance with the present invention;

[0025]FIG. 2 is a schematic view of a second embodiment of avaporization system according to the present invention;

[0026]FIG. 3 is a side sectional view of a second embodiment of avaporizer;

[0027]FIG. 4 is a perspective view of a third vaporizer embodiment;

[0028]FIG. 5 is a side sectional view of a fourth embodiment of avaporizer;

[0029]FIG. 6 is a side sectional view of a fifth embodiment of avaporizer;

[0030]FIG. 7 is a side sectional view of a sixth embodiment of avaporizer;

[0031]FIG. 8 is a side sectional view of a seventh embodiment of avaporizer;

[0032]FIG. 9 is a perspective view of an eighth embodiment of avaporizer;

[0033]FIG. 10 is a sectional view of a vaporizer for use in a microbialdecontamination process, illustrating another embodiment of the presentinvention;

[0034]FIG. 11 is an enlarged sectional view of a portion of a vaporizerheating tube comprised of granular metal particles embedded within anelectrically non-conductive material;

[0035]FIG. 12 is an enlarged sectional view of a portion of a vaporizerheating tube comprised of metal flakes embedded within an electricallynon-conductive material;

[0036]FIG. 13 is an enlarged sectional view of a portion of a vaporizerheating tube comprised of metal coated glass spheres embedded within anelectrically non-conductive material;

[0037]FIG. 14 is an enlarged view of the area shown in FIG. 14;

[0038]FIG. 15 is an enlarged sectional view of a vaporizer for use in amicrobial decontamination process, according to still another embodimentof the present invention;

[0039]FIG. 16 is an enlarged sectional view of a vaporizer for use in amicrobial decontamination process, according to still another embodimentof the present invention;

[0040]FIG. 17 is an enlarged sectional view of a vaporizer for use in amicrobial decontamination process, according to still another embodimentof the present invention;

[0041]FIG. 18 is a sectional view of a vaporizer including a microwavegenerator, according to yet another embodiment of the present invention;

[0042]FIG. 19 is a sectional view of a vaporizer for use in a microbialdecontamination process, according to yet another embodiment of thepresent invention;

[0043]FIG. 20 is a sectional view taken along lines 20-20 of FIG. 19;

[0044]FIG. 21 is a perspective view of a vaporizer heating tube sectioncomprised of electromagnetically responsive material embedded in anelectrically non-conductive material, according to a still furtherembodiment of the present invention;

[0045]FIG. 22 is a perspective view of a vaporizer heating apparatusformed from two heating tube sections of the type shown in FIG. 21;

[0046]FIG. 23 is a sectional view of a portion of a vaporizer heatingapparatus assembly, according to a still further embodiment of thepresent invention; and

[0047]FIG. 24 is an exploded perspective view of the vaporizer heatingapparatus assembly shown in FIG. 23.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0048] Referring now to the drawings wherein the showings are for thepurposes of illustrating a preferred embodiment of the invention onlyand not for purposes of limiting same, FIG. 1 shows a system forproviding an antimicrobial vapor to a sterilization chamber or formicrobially decontaminating a room or other defined area with anantimicrobial vapor. While the system is described with particularreference to steam and to hydrogen peroxide in vapor form, otherantimicrobial vapors are also contemplated, such as vapors comprisingperacetic acid or other peroxy compounds, aldehydes, such asformaldehyde vapors, and combinations of vapors, such as hydrogenperoxide with peracetic acid, and the like.

[0049] While particular reference is made to sterilization, which refersto the destruction of all microorganisms, whether harmful or not, it isto be appreciated that the antimicrobial vapor is alternatively used toprovide lesser levels of microbial decontamination, such as disinfectionor sanitization. The term “microbial decontamination” and similar terms,as used herein, include the destruction of microorganisms, such asbacteria and fungi. The term is also intended to encompass thedegradation or deactivation of other harmful microorganism-sizedbiological species, and smaller replicating species, particularly thosecapable of undergoing conformational changes, such as prions.

[0050]FIG. 1 illustrates a system particularly suited to the generationof steam under pressure for a steam sterilizer 10. The system includes avapor generator, such as a flash vaporizer 12, in close proximity to achamber 14 of the sterilizer 10. Items to be microbially decontaminatedare loaded into the chamber 14 through an opening 16 closed by a door18. Steam from the generator 12 is supplied both to the interior chamber14 and to a heating jacket 20, which surrounds the chamber. The systemis supplied via piping, such as thermally insulated tubes or passageways22 and 24, respectively.

[0051] The generator 12 includes an induction vessel 28, which ispositioned in a magnetic field and is heated by electric currentsinductively generated in the induction vessel by the magnetic field. Theinduction vessel 28 transfers heat generated to the liquid to bevaporized, either by conduction, radiation, or convection, which causesthe liquid to be converted to vapor.

[0052] In a first embodiment, shown in FIG. 1, the induction vessel 28comprises a heating tube 30. The heating tube 30 has a hollow tube wall32 defining an interior passage or bore 34, which is preferablycylindrical in shape. The tube 30 is formed from an electrically andthermally conductive material, such as iron, carbon steel, stainlesssteel, aluminum, copper, brass, bronze, electrically conductive ceramicand polymer composites, or other materials capable of being inductivelyheated. As further described below, the bore 34 provides a chamber forreceiving a liquid, such as water, to be converted to a vapor, such assteam. The bore 34 is sized to receive a volume of water that issufficiently small to be vaporized rapidly as it enters and contactswalls of the bore in a flash vaporization process. While the bore 34 isshown in FIG. 1 as being vertically aligned along its axis, it is to beappreciated that the bore is alternatively horizontally aligned or haveportions of the bore which are arranged in different orientations, as isdiscussed in further detail below. An induction coil 36 is wrappedaround an outer surface 38 of the tube 30 in a helix, along all or aportion of the tube length. The coil 36 is preferably spaced from thetube by a layer 40 of thermal insulation material. An electricallyinsulative housing 42 surrounds the coil and insulation material.

[0053] An upper end or outlet 44 of the heating tube 30 is fluidlyconnected with the tubes 22, 24. Valves 46, 48 in the tubes 22, 24variably adjust the amount of steam passing to the chamber 14 andheating jacket 20, respectively. The tubes, 22, 24, or a fitting (notshown) connecting the piping with the heating tube 30, may be formed ofmaterials, such as copper, brass, or polymeric pipes.

[0054] An AC source 50 supplies an alternating current to the coil 36.In response to the applied current, the coil 36 produces an alternatingmagnetic field, which passes through the heating tube 30, causing eddycurrents which heat the tube. The heat passes through to an innersurface 52 of the tube 30 in contact with the water droplets movingthrough the bore 34. The electrical current, and hence the rate ofheating of the heating tube 30, is adjustable, for example, by theprovision of an adjustment means 54, such as a pulse width modulator, avariable resistor, or the like in an electrical circuit 56 connectingthe AC source 50 and the induction coil 36. Alternatively, oradditionally, the adjustment means includes a simple on/off switch 58 inthe circuit 56.

[0055] The current adjustment means 54, 58 are preferably under thecontrol of a control system 60, which also controls other aspects of thesterilization system. For example, the control system 60 receives steamtemperature measurements from a temperature monitor 62, such as athermocouple, positioned adjacent the outlet end of the heating tube, orelsewhere in the system such as in the passages 22, 24. The controller60 controls the current adjustment means 54, 58 in response to themeasured temperature to maintain a preselected steam temperature. Thecontroller 60 is preferably also connected with one or more oftemperature monitors 64 and pressure monitors 66, 68 positioned withinthe chamber 14, the heating jacket 20, or elsewhere in the system. Thecontroller regulates the generator 12 to maintain desired sterilizationtemperature and pressure, as is described in greater detail below.

[0056] Fresh water or other liquid to be vaporized from a source 70 suchas mains water or purified water from a tank, is supplied to thegenerator via a liquid inlet tube or line 72, regulated by an adjustableinlet valve 74, such as a solenoid valve, which is preferably under thecontrol of the controller 60. The inlet tube 72 is connected to a secondend or inlet end 76 of the heating tube 30. As with the outlet tubes 22,24, the inlet tube 72, or a fitting (not shown) connecting the inlettube 72 with the heating tube 30, is preferably formed from copper,brass, or polymeric pipe. A check valve 78 in inlet line 72 ispreferably provided to prevent the backflow of water out of the steamgenerator 12.

[0057] The inductively generated heat flash vaporizes the water locatedin the bore 34 to produce steam. The water is preferably introduced tothe bore as a continuous stream of liquid water under pressure. Thewater is changed to steam as it traverses a two-phase region from asaturated liquid to a saturated gas. As steam is produced, the pressureinside the bore 34 increases. The steam is forced under pressure out ofthe bore and through the fluid pathway 24 connecting the generator 12 tothe chamber 14. The process continues in this manner, producing moresteam from the series of water injections.

[0058] In an alternative embodiment, the water, or other liquid to bevaporized, is introduced as a continuous stream.

[0059] If mains water is used, the water is preferably passed through afilter system (not shown) to remove particulate material, dissolvedminerals, and/or organic matter. Purity can be expressed as theresistance between two electrodes spaced one centimeter apart in asample of water to be tested, one meg-ohm being a resistance of 1×10⁶ohm. Preferably, the filtered or otherwise purified water has a purityof 1 meg-ohm, or higher, which may be achieved with a reverse osmosis(RO) filter followed by an ion-exchange bed. Optionally, a pump 80pressurizes the water in the inlet line 72.

[0060] Spent steam or liquid water exits the sterilizer chamber 14through a line 90. A steam trap 92 in the line 90 opens when condensateis present to release the condensate. Spent steam or liquid water fromthe jacket 20 leaves by an interconnected drain line or by a separatesecond drain line 94 and trap 96. Thermal insulation 98, optionallysupplemented by heating tape or other heating means (not shown) whereappropriate, preferably surrounds the pathways 22, 24, the heatingjacket 20, and may also cover the door 18.

[0061] Optionally, a suction means 100, such as a vacuum pump or waterejector, is used to withdraw air or steam from the chamber 14, via avacuum line 102, prior to a sterilization cycle, during the cycle, or toremove spent vapor after the sterilization cycle.

[0062] A typical sterilization process proceeds as follows. Items to bemicrobially decontaminated, such as medical, dental, or pharmaceuticalinstruments, or the like, are loaded into the chamber 14 and the door 18closed. Steam is introduced to the chamber 14 to displace air, whichpasses downward and out of the chamber via the drain line 90. Thecontroller 60 optionally controls the vacuum pump or water ejector 100to withdraw air from the chamber 14. The controller 60 then closes valve104 in the vacuum line 102. Optionally, several pulses of steam areapplied to chamber 14, each one followed by or preceded by a vacuumpulse. For example, steam is introduced until a preselected pressure isachieved. The pump or water ejector 100 is then operated until apreselected vacuum is achieved. The pressurizing and evacuating stepsare preferably repeated several times (usually about four times), endingwith a steam pressurizing step.

[0063] The controller also controls the heating of the interior of thechamber by controlling operation of the generator and valve 48.Specifically, the controller receives temperature measurements from thetemperature monitors 64, 68 and controls the water inlet valve 74 and/orvariable resistor 54 to generate steam, which passes along the line 24to the jacket. Once the chamber 14 is at a suitable temperature,preferably above the condensation temperature of the steam, thecontroller 60 opens the valve 46, allowing steam to enter the chamber.The controller 60 controls operation of the resistor 54 and variousvalves 46, 48, 74, 96, 104, in response to temperature and pressuremeasurements received from the monitors 62, 64, 66, 68, to maintainpreselected sterilization conditions (e.g., temperature and pressure)for a period of time considered sufficient to effect the desired levelof antimicrobial decontamination. Once the period of time has elapsed,valve 46 is closed and the steam is withdrawn from the chamber 14 by thevacuum pump 100. Fresh or filtered air is then allowed to enter thechamber 14.

[0064] In an alternative embodiment, shown in FIG. 2, the sterilizationsystem 10 is shown adapted for microbial decontamination with hydrogenperoxide or other multi-component vapor. In this embodiment, thegenerator 12 is analogous to that of FIG. 1 but is used for theproduction of a multi-component vapor, such as a hydrogen peroxide andwater vapor mixture. A liquid to be vaporized, such as an aqueousmixture of hydrogen peroxide in water, is pumped from a reservoir ortank 70 to the generator via the inlet line 72. More specifically, ameans for introducing liquid hydrogen peroxide, such as an injectionpump 80, pressurized container, gravity feed system, or the like,deposits hydrogen peroxide, preferably in the form of a liquid flow orspray, from the reservoir 70 into the generator 12 via an injectionnozzle 108.

[0065] The liquid hydrogen peroxide includes a mixture of hydrogenperoxide in a diluent, such as water, preferably an aqueous mixturecomprising about 30-40% by weight hydrogen peroxide in water.

[0066] The hydrogen peroxide vapor generated when the liquid contactsthe heated wall 32 of the heating tube 30 is preferably mixed with acarrier gas. In one embodiment, a carrier gas, such as air, nitrogen,carbon dioxide, helium, argon, or a combination of carrier gases, is fedinto the flash vaporizer 12 concurrently with the hydrogen peroxideliquid to assist in propelling the peroxide vapor through the vaporizer.The air enters the heating tube 30 via a carrier gas line 110, which maybe connected with the liquid inlet line 72, as shown in FIG. 2, or passdirectly into the bore 34. Alternatively, or additionally, a carrier gasline 112 is connected with the outlet line 22, such that the carrier gasmixes with the already formed vapor. Mixing all or most of the carriergas with the vapor after vapor formation increases the throughput of thevaporizer. Valves 114, 116 in the carrier gas lines 110, 112 are used toregulate the flow rate of carrier gas through the lines 110, 112,respectively.

[0067] The carrier gas may be air at atmospheric pressure or suppliedfrom a tank or other reservoir (not shown). Preferably, the incomingcarrier gas is passed through a filter 120, such as an HEPA filter, toremove airborne particulates, through a dryer 122 to remove excessmoisture, and is heated by a heater 124 to raise the temperature of thecarrier gas.

[0068] The preferred pressure of the carrier gas supplied to lines 110,112 varies with the production rate of hydrogen peroxide and the lengthand restrictiveness of passages in the flash vaporizer 12, and typicallyvaries from 1.0-2.0 atmospheres absolute (1.013×105−2.026×105 Pascalsabsolute), i.e., about 0-1 atm. gauge (0-1.013 ×105 Pascals gauge), morepreferably, about 6-14×103 Pa.

[0069] The flash vaporization and sweeping carrier gas ensure that thehydrogen peroxide/water mixture does not condense and form a puddle inthe vaporizer. Another advantage of using such a carrier gas to carrythe liquid and vapor through the generator 12 arises because the liquidhydrogen peroxide is likely to continuously impinge on the same point inthe vaporizer 12. The more dispersed the liquid hydrogen peroxide iswithin the vaporizer, the more readily the peroxide will be vaporized.In addition, with a well-dispersed hydrogen peroxide injection, it isless likely that specific regions of the vaporizer will experience unduecooling thereby hindering the vaporization process.

[0070] The carrier gas tends to cool the vaporizer, reducing the rate atwhich the aqueous hydrogen peroxide solution is vaporized. Consequently,it is desirable to maintain the carrier gas at or slightly above aminimum flow rate needed to carry the vaporized hydrogen peroxidethrough the vapor generator 12 without significant degradation of theperoxide vapor, but at a flow rate which is low enough such thatappreciable cooling of the vaporizer by the carrier gas does not occur.Accordingly, the flow rate of carrier gas through the vapor generator 12is preferably lower than the flow rate of carrier gas which does notpass through the vapor generator 12. The majority of the carrier gasthus travels through the passage 112 and is injected into the secondcarrier gas stream at a mixing zone 126 downstream of the vaporizer 12,where both the carrier gas stream and the vapor are combined prior toentering the chamber 14.

[0071] The mixture of carrier gas and vapor hydrogen peroxide passesthrough line 22 and into the chamber 14. A sensor 128, such as ahydrogen peroxide sensor, optionally detects the concentration ofhydrogen peroxide and/or water vapor in the chamber 14. The controllerreceives the detected concentration measurements or signals indicativethereof and temperatures and pressures from monitors 64, 66 andregulates the supply of fresh hydrogen peroxide vapor to the chamber orother operating conditions accordingly. Alternatively, the controller ispreprogranmed with expected concentrations of hydrogen peroxide or otherdata which allows the controller to maintain selected chamber conditionsby controlling and/or measuring various parameters of the system, suchas chamber temperature and pressure, hydrogen peroxide and carrier gasflow rates, and the like.

[0072] Spent vapor exits the chamber 14 via an outlet line 102 and ispreferably passed through a destroyer 130, such as a catalyticconverter, to convert any remaining hydrogen peroxide to oxygen andwater, before releasing it to the atmosphere.

[0073] Alternatively, the outlet line 102 is coupled with the carriergas inlet line(s) 110, 112 as a recirculating flow through system,whereby the spent vapor, preferably after passing through the catalyticconverter, is returned to the inlet line 110, intermediate the filter120 and dryer 122, or prior to the filter, such that the spent vapor isdried and heated before mixing once more with the hydrogen peroxideliquid or vapor.

[0074] In this embodiment, the sterilizing vapor, hydrogen peroxide andwater in the preferred embodiment, is effective at room temperature orabove room temperature and at atmospheric, subatmospheric, or aboveatmospheric pressures. The steam heating jacket 20 and line 24 arepreferably eliminated, and, if it is desired to heat the chamber 14, aheater 131, such as a resistance heater, surrounds all or part of thechamber. The heater 131 is preferably under the control of thecontroller 60.

[0075] It is generally desirable to maintain the hydrogen peroxide belowits saturation point to avoid condensation on the items to besterilized. Thus, the controller 60 preferably controls the chamberconditions, such as temperature, pressure, vapor introduction rate, andso forth to maintain the hydrogen peroxide concentration close to butslightly below, its saturation level. For example, the control system 60includes a comparator 132 (see FIG. 2) for comparing the monitoredcondition signals from the monitors 128, 64, 66 with preselected idealhydrogen peroxide vapor concentration and other conditions as indicatedby reference signals. Preferably, the comparator determines a deviationof each monitored condition signal from the corresponding referencesignal or a reference value. Preferably, a plurality of the conditionsare sensed and multiple comparators are provided. A processor 134addresses an algorithm implementing program or pre-programmed look uptable 136 with each deviation signal (or combination of deviations ofdifferent conditions) to retrieve a corresponding adjustment for theflash vaporizer 12. Other circuits for converting larger deviations tolarger adjustments and smaller deviations to smaller adjustments arealso contemplated. Alternately, the error calculation can be made atvery short intervals with constant magnitude increases or decreases whenthe monitored condition is below or above the reference points.

[0076] The adjustment values are used by the controller 60 to adjust thehydrogen peroxide metering pump 80 and the carrier gas regulators 114,116 to bring the monitored conditions to the reference values. Forexample, vapor injection rates are increased when a lower than desirablevapor concentration, higher temperatures, higher pressure, or the likeis detected. Vapor production rates are reduced in response to highersensed vapor concentration, lower sensed temperatures, lower pressure,and the like.

[0077] The vapor hydrogen peroxide system can be operated as an ambientor above atmospheric pressure system, in which the carrier gas andhydrogen peroxide vapor within the chamber is continually orintermittently replenished. Or, the system may be operated as a deepvacuum system, in which the chamber 14 is evacuated to a pressure of,for example about 10 torr or below, prior to introduction of hydrogenperoxide. As with the steam vapor system, one or more pulses of vapormay be introduced to the chamber 14, with vacuum pulses between them. Inother respects, the system of FIG. 2 is analogous to the system of FIG.1 and is operated in a similar manner. For sterilizing larger enclosures14, such as rooms, additional vaporizers 12 may be employed, each oneseparately under the control of the controller 60.

[0078] It will be appreciated that while the multi-component vapor hasbeen described with particular reference to hydrogen peroxide, othersingle component and multi-component vapors are also contemplated. Othersuitable sterilizing vapors include peracids, such as peracetic acidwith water, a mixture of hydrogen peroxide with peracetic acid, and thelike.

[0079] With reference now to FIG. 3, an alternative embodiment of avapor generator 12 is shown. Similar components are identified by thesame numerals and new components are given new numbers. In thisembodiment, in place of a heating tube, the induction vessel 28 includesa bore 34 which is formed by drilling or otherwise forming a passage ina block 140 of an electrically conductive material, such as graphite,aluminum, copper, brass, bronze, steel, or the like. A coil 36inductively heats the block 140 when an AC current is passed through thecoil. Alternatively, the bore 34 is defined within tubing 142 mountedwithin the block 140 and in thermal contact therewith. The tubing 142may be formed from a thermally-conductive material such as copper,brass, a polymer or a filled polymer. Alternatively, in place of tubing,the walls of the bore 34 defined by the block 140 may be coated with alayer (not shown) of a thermally conductive, protective material such asstainless steel, TEFLON™ glass, or the like, which is resistant to theliquid and vapor passing through the bore but need not be inductivelyheated by the coil 36. In these embodiments, heat passes from the blockto the liquid by conduction through the tubing 142 or thermallyconductive layer.

[0080] The induction coil 36 encircles the block 140 or a portionthereof and induces the block to heat up in a similar manner to theheating tube 30 of FIG. 1. Heat flows from the block 140 and through thetubing 142, where present. As with the embodiments of FIGS. 1 and 2, theliquid to be vaporized, e.g., aqueous hydrogen peroxide or water, eitheralone or with a carrier gas, passes through the generator bore 34 and isvaporized when it comes into contact with the heated walls 54 of thebore. As with the prior embodiments, thermal insulation material 40 ispacked between the coil 36 and the block 140 and between the coil andthe housing 42. In the case of hydrogen peroxide, the block 140 ismaintained by operation of the induction coil 36 at a temperature belowthat at which significant dissociation of the hydrogen peroxide occurs.Optionally, an overtemperature device 144 is mounted on or in the block140 and shuts down the power to the coil 36 in the event the coil isenergized without sufficient vaporizable liquid in the block 140. Inaddition, a pressure release valve 146 is provided between the block 140and the sterilization chamber 14, which releases excess pressure toprotect the block and the chamber 14 from overpressure conditions.

[0081] In the embodiment of FIG. 3, the bore 34 comprises a series ofelongate bore portions 150, 152, 154, 156, and 158 (four are shown inFIG. 3, although fewer or greater than four bore portions are alsocontemplated), which pass generally longitudinally back and forththrough the block 140. The bore portions are connected by connecting orend portions 160, 162, 164, which may be positioned outside the block140 for convenience of manufacture. End walls 168 of the end portions160, 162, 164 are positioned generally at right angles to the directionof flow of the liquid in the bore portions. The greater inertia offlowing liquids and droplets thrown against the end walls 168, with eachturn, thereby increases the rate of vaporization and reduces the chancethat unvaporized droplets will be discharged from the vaporizer.

[0082] Optionally, as shown in FIGS. 4 and 5, the bore 34 increases indiameter along its length, either stepwise, with each successive boreportion 152, 154, 156 (FIG. 4), or progressively, along its length (FIG.5), thus creating an increasing area of contact and internal volume perunit length. The liquid hydrogen peroxide contacts the wall surfaces 52of the bore 34 and is vaporized. The increasing volume of thevapor/liquid mixture passing through the bore 34 is accommodated by theincreasing diameter of the bore portions 150, 152, 154, 156, etc.

[0083] In each of the embodiments, the bore 34 may make several turnswithin the block 140. For example, starting at the bore inlet 76, thebore 34 makes a U-turn adjacent one end 170 of the block, returns to aninlet end 172 of the block, and optionally makes one, two, or more suchturns before reaching the outlet 44. In one embodiment the turns areformed by sharp, “L-shaped” rather than rounded turns. For example, asshown in FIG. 3, each turn includes two approximately 90 degree cornersadjoining the end wall 168, which turn the bore through approximately180 degree. Having generally sharp, rather than rounded cornersencourages the flowing liquid/vapor mixture to hit the walls, therebyimproving the rate of vaporization.

[0084] Other arrangements are contemplated, such as a spiral bore 34, asshown in FIG. 6. At each turn, inertia tends to propel fine, suspendeddroplets into the walls resulting in the vaporization of the droplets.In this manner, any fine droplets of mist or fog are turned to vapor.Preferably, at least two substantially 180 degree turns are provided inthe flowpath to ensure this increased contact.

[0085] Other arrangements for progressively increasing the bore diameterare also contemplated. In the embodiment of FIG. 7, the number of boreportions increases with each pass through the block. For example, asingle longitudinal bore portion 150 defines the first pass, and two ormore bore portions 152A, 152B define the second pass. Each of the secondbore portions 152A, 152B is preferably connected with two more boreportions 154A, 154B or 154C, 154D for a third pass, and so forth. Inthis way, as for the earlier embodiments, the cross sectional area ofthe fluid pathway 34 created by the bore portions increases as thehydrogen peroxide travels from the inlet 76 to the outlet 44 (in thiscase, a plurality of outlets).

[0086] Other methods for increasing the heated surface area and/orcreating turbulence which brings the liquid into contact with the heatedsurface and encourages mixing with the carrier gas are alsocontemplated. In the embodiment of FIG. 8, a deflecting member or insert180 in the shape of a helix or auger is axially mounted within the bore34. The insert 180 is preferably inductively heated as well as or inplace of the tube 30 (or block 140, where present). For example, thehelix 180 is formed from stainless steel or other electricallyconductive material which is not susceptible to degradation by theliquid or vapor passing through the bore. In the embodiment of FIG. 8,turns 181 of the corkscrew increase in diameter in the direction offlow. For example, the last turn is close to or touching the tube 30.

[0087] In an alternative embodiment, shown in FIG. 9, an insert 180 isaxially mounted in the bore 34 and includes axially spaced disks orplates 182 mounted to a central shaft 184. In yet another embodiment,baffles or fins may be provided to reduce the available flow space whileincreasing the heated surface area. For example, as shown in FIG. 2,baffles 186 extend from the walls of the tube into the bore. The bafflesmay transfer heat by conduction and/or may be inductively heated in thesame manner as the tube 32.

[0088] To increase heat flow to the insert 180 in the embodiments ofFIGS. 8 and 9, the insert is preferably attached to the tube 30 bythermally conductive members 188, such as metal screws (FIG. 8). Forexample, threads are tapped in the tube 30 and adjacent ends of theinsert 180. Thermally conductive screws are then inserted throughcorresponding tapped threads and thus create a path for the travel ofheat to the insert. Countersinking the heads of the screws and/orsoldering or brazing over the screw heads creates a smooth surface whichallows the induction coil 36 to be closely spaced from the tube 30.

[0089] The water, liquid hydrogen peroxide, or other vaporizable liquid,vaporizes as it contacts the wall surface 52 of the bore 34 and isprogressively converted from a liquid, spray, or mist to a vapor. Theincreasing pressure which would normally result from this conversion issubstantially eliminated by the increase in size of the bore and/or byan increase in flow velocity such that the flow through the bore ismaintained. At the end of the series of passes through the bore 34, thewater and/or hydrogen peroxide is preferably entirely in vapor form at atemperature and pressure which maintain the vapor below the dew point,such that condensation of the vapor does not occur.

[0090] The vaporizer 12 is capable of achieving a higher vapor outputthan conventional, drip-type vaporizers which are heated by aresistance-type heater. The heating rate which can be achieved using aninduction coil 36 is significantly higher than that which can beachieved with resistance heaters. Obviously, as the heat suppliedincreases, correspondingly higher outputs can be achieved.

[0091] It will be appreciated that the vapor generator of any of theabove embodiments is alternatively coupled with a large enclosure, suchas a room, or temporary enclosure surrounding a large item to bemicrobially decontaminated. This is particularly true when a sterilantvapor, such as hydrogen peroxide, is used which is effective at or aboutroom temperature (i.e., from about 15-30° C.) and at or close toatmospheric pressure.

[0092] Sterilizable enclosures include microorganism-free or nearmicroorganism-free work areas, freeze dryers, and pharmaceutical or foodprocessing equipment. Whether high sterilization temperatures and/orevacuation of the enclosure during sterilization are feasible depends onthe construction of the enclosure and the nature of its contents. Forexample, sterilizable work areas are, in some instances, constructed ofnon-rigid plastic materials which do not withstand high temperatures andlarge pressure gradients. Food processing equipment, in contrast, isoften required to withstand high temperatures and pressures duringprocessing operations and is more easily adapted to achieving optimalsterilization conditions through evacuation and heating. sing one ormore of such vaporizers 12, a high speed bottling line (e.g., about 1000bottles/min) can be decontaminated.

[0093] For example, the chamber 14 may be a room having a volume on theorder of 1,000-4,000 cubic meters. In this embodiment, the combinedcarrier gas streams may have a flow rate of about 20,000 liters/minute,while the carrier gas stream flowing through the vaporizer 12 is 100liters/min or less, more preferably, about 20 liters/min or less, mostpreferably, about 1-10 liters/min.

[0094] Optionally, the pathways 22, 24, 102 include all or a portion ofthe duct work of a pre-existing HVAC system. Upon initiating adecontamination process, air from the room is circulated through thedryer 122 for a sufficient duration to bring the relative humidity inthe room down to an acceptable level, preferably below 20% relativehumidity. For sealed enclosures, pressure control within the enclosuremay be appropriate. For decontamination of clean rooms and the like,where drawing potentially contaminated air into the room is to beavoided, the pressure in the room is preferably maintained above ambientpressure. Where hazardous materials have been used or exposed in theroom to be treated, a below atmospheric pressure is preferablymaintained in the room 14 to ensure that the hazardous materials do notescape prior to decontamination.

[0095] Once the room 14 has been brought to a sufficiently low relativehumidity, an antimicrobial vapor is injected into the air. Theantimicrobial vapor includes hydrogen peroxide vapor in one embodiment,although other antimicrobial vapors or mixtures of antimicrobial vaporsare also contemplated.

[0096] The controller 60 is connected with one or more peroxideconcentration sensors 128 in the room. The controller optionallycontrols fans (not shown) or other devices in the room 10 for adjustingthe distribution of hydrogen peroxide vapor for better uniformity.

[0097] When the air recirculation ducts are larger in diameter and havea higher air moving capacity, a second flash vaporizer 12 and a secondinjection pump 80 are connected with the liquid peroxide source 70 andwith the air source. For larger enclosures, one or more additional aircirculation lines with flash vaporizers are provided.

[0098] While described with particular reference to hydrogen peroxide,it will be appreciated that the system of the present invention is alsoapplicable to vaporization of other solutions and pure liquids, such asperacetic acid, other peroxy compounds, and the like.

[0099] A plurality of further contemplated embodiments of the presentinvention will now be described with particular reference to FIGS.10-24. In accordance with the further contemplated embodiments of thepresent invention, a vaporizer heating apparatus comprised of a heatingtube and/or an insert that includes an electrically non-conductivematerial and an electromagnetically responsive material, as will bedescribed in detail below. It should be understood that in each of thefurther contemplated embodiments, the insert is optionally provided. Theterm “electromagnetically responsive material” is used herein to referto a material that responds to the presence of an electric field, amagnetic field or both, such that thermal energy is produced uponexposure to at least one of the aforementioned fields. The electric andmagnetic fields may be static or oscillatory.

[0100] The further contemplated embodiments of the present invention maytake a variety of forms, including, but not limited to, those discussedin detail below. According to one further contemplated embodiment, tube30 and/or insert 180 is/are comprised of an electrically non-conductivematerial and an electromagnetically responsive material, wherein theelectromagnetically responsive material is embedded in the electricallynon-conductive material. In another further contemplated embodiment, alayer of electromagnetically responsive material may provide an externalsurface of tube 30 and/or insert 180, or may be located inside of anelectrically non-conductive material. In still another furthercontemplated embodiment, a layer of electrically non-conductive materialisolates the electromagnetically responsive material from antimicrobialfluids. In this regard, an electrically non-conductive material is usedto provide a protective coating layer.

[0101] It should be appreciated that elements of the foregoingcontemplated embodiments may be used in alternative combinations.Illustrative embodiments are described in detail below.

[0102] The electrically non-conductive material may take many suitableforms, including, but not limited to, a polymeric material, a ceramicmaterial or a glass. Furthermore, a polymer, a ceramic and/or a glassmay be used in combination to form tube 30 and/or insert 180.

[0103] Suitable polymers include, but are not limited to, athermoplastic polymer or a thermoset polymer.

[0104] By way of example, and not limitation, a thermoplastic polymerforming the electrically non-conductive material may be selected fromthe group consisting of: a nylon; Amodel® (PPI, polyphthalanide); Aurum®(polyimide); Ryton®/Fortron® (PPS, polyphenylenesulphide);Fluoropolymers (PFA, FEP, Tefzel® ETFE, Halar® ECTFE, Kynar® PVDF);Teflon® PTFE; Stanyl® (4.6 polyamide, 4.6 Nylon); Torlon®(polyamide-imide); Ultem® (polyetherimide, PEI); Victrex® PEEK(polyaryletherketone, polyetheretherketone); or any other thermoplasticpolymers having a “use temperature” above the highest temperature neededto produce an antimicrobial vapor. As indicated above, the antimicrobialvapor may be produced from water alone, or a mixture of fluids such aswater and hydrogen peroxide. In most cases, it is expected thatthermoplastic polymers having a use temperature above about 150° C.should be suitable. For example, nylons have a short term usetemperature of about 199° C. For certain sterilants, heat stabilizednylon 6/6, which has a continuous use temperature of 121° C., may besufficient. Teflon has a continuous use temperature of 260° C.

[0105] The thermoset polymer forming the electrically non-conductivematerial may be selected from the group including, by not limited to, anepoxy or a urethane.

[0106] By way of example, and not limitation, a suitable ceramicmaterial for forming the electrically non-conductive material may beselected from the group consisting of: silica, alumina, magnesia orother metal-oxide based materials.

[0107] The electromagnetically responsive material may take manysuitable forms, including, but not limited to, a metal or metal alloy, ametal coated material, carbon, graphite, stainless steel, a metal alloysolder (e.g., tin and zinc), a ferromagnetic material (e.g., iron), aferrimagnetic material (i.e., ferrites, such as magnetite (Fe₃O₄) orFeO.Fe₂O₃), a ferroelectric material (such as perovskites, e.g., leadtitanate (PbTiO₃)), a ferrielectric material, and combinations thereof.

[0108] By way of example, and not limitation, the metal may be selectedfrom the group consisting of: nickel, copper, zinc, silver, stainlesssteel, tungsten, nichrome (nickel-chromium alloy), and combinationsthereof.

[0109] As indicated above, a metal alloy solder can be used as anelectromagnetically responsive material. The solder melts duringprocessing of the electrically non-conductive material (e.g., a polymer,a ceramic or glass) to form an interconnecting metallic network withinthe electrically non-conductive material. In the case of a polymer, alow melting solder is combined with the polymer resin and processed. Forexample, a polymer and a low melting solder can be extruded intostrands. The strands are cooled and chopped into pellets. The pelletsare then injection molded into a heating tube and/or insert. The lowmelting solder forms an interpenetrating metallic network within thepolymer.

[0110] In the case of a ceramic, the porosity of the ceramic allows thesolder to flow within the ceramic when the ceramic is calcined, thusproducing a calcined ceramic having a metallic network. Thepre-calcining porosity of the ceramic helps the solder to flow withinthe ceramic during calcining. It should be appreciated that the soldershould have a melt temperature that is above the highest temperatureneeded to vaporize the antimicrobial fluids.

[0111] Metals other than solder can also be used to produce the metallicnetwork. In this regard, any metal that will melt when the ceramic iscalcined is also suitable. Since the calcining temperature of mostceramics is typically in the range of 2,500° F. to 3,000° F., mostmetals will melt during calcining. Upon cooling, the metalre-crystallizes forming an interpenetrating, metallic network within theceramic.

[0112] Carbon is also a suitable electromagnetically responsive materialfor use with a polymer, a ceramic or glass matrix. In this regard,carbon can be added to the polymer, ceramic, or glass to produce anetwork of conductive carbon particles. Since carbon is also arefractory, the carbon particles will withstand the high calciningtemperatures of the ceramic. Carbon is also thermally conductive, andthus will help to diffuse heat (produced by induction heating). Thecarbon also provides a good receiving “antenna” for electromagneticwaves.

[0113] As discussed above, one further contemplated embodiment of thepresent invention includes a tube 30 and/or insert 180 that arecomprised of an electrically non-conductive material and anelectromagnetically responsive material, wherein the electromagneticallyresponsive material is embedded in the electrically non-conductivematerial (e.g., a polymer, a ceramic or a glass matrix) to form acomposite material. The electromagnetically responsive material may takethe form of a particulate, including, but not limited to fibers, flakes,spheres, whiskers, grains or combinations thereof, wherein theparticulate is a metal or metal alloy, a metal coated particle, carbon,or graphite. The particulate may take a variety of shapes, including,but not limited to, spherical, oblate and prolate. Furthermore, theelectromagnetically responsive material may alternatively coat aparticulate (i.e., metal or metal alloy, carbon or graphite coatedparticulates).

[0114] Examples of specific suitable particulates, include, but are notlimited to, carbon particulates (fibers, flakes, whiskers or grains);nickel particulates (fibers, flakes, whiskers, or grains); tungstenparticulates (fibers, flakes, whiskers or grains); nichrome (wires,fibers, flakes, whiskers, or grains); nickel, copper or silver coated(autocatalytically or by electrodeposition) glass spheres; nickel,copper or silver coated (autocatalytically or by electrodeposition)thenioplastic polymer particulate; steel flakes; and stainless steelfibers.

[0115] In one embodiment, the electromagnetically responsive particulateis embedded in the electrically non-conductive material in aconcentration suitable to provide a heating apparatus having a desiredheating characteristic. As will be appreciated, the heat generating andheat transfer characteristics of the heating apparatus are based uponthe concentration (i.e., loading) of electromagnetically responsiveparticulate within the electrically non-conductive material. It isbelieved that the heat transfer (i.e., thermal conductivity)characteristics of the heating apparatus are related to the electricalconductivity characteristics of the heating apparatus. Accordingly, theconcentration of the electromagnetically responsive particulate in theheating apparatus may be determined in accordance with percolationtheory.

[0116] According to percolation theory, when the concentration of theelectromagnetically responsive particulate reaches the percolationthreshold, the electrical conductivity of the composite will riseprecipitously. Therefore, when rapid heating is desired, theconcentration of the electromagnetically responsive particulate ispreferably at or above the percolation threshold. Likewise, if a longerheating time is desired or acceptable, then the concentration of theelectromagnetically responsive particulate may be below the percolationthreshold.

[0117] In the case of a particulate loaded composite, the mathematicalmodel that describes the electrical behavior of the composite is knownas percolation theory. For example, if particles of metal are depositedon a substrate in an L×L array of holes, electrical conduction can occurbetween the metal particles, because when two adjacent holes are filledwith a metal particle, they just barely touch each other, therebyallowing electrical conduction between the metal particles. Groups oftouching metal particles are referred to as “clusters.” A cluster whichextends from one end of the array to the other is called a “spanningcluster.”

[0118] When metal particles are initially deposited into the holes ofthe L×L array there can be no electrical conduction. In this regard,electrical conduction cannot occur until at least L metal particles havebeen deposited. However, in view of the statistical probability of Lmetal particles aligning themselves to form a spanning cluster, manymore than L metal particles will need to be deposited before theprobability of a spanning cluster becomes significant. At some pointthere is an exponential increase in the electrical conduction. The“percolation threshold” is the concentration of electromagneticallyresponsive particulate that results in an electrically conductivecomposite.

[0119] The percolation threshold depends on the aspect ratio (i.e., theratio of the longest dimension to the shortest dimension) of theparticulate. In this respect, it is believed that the percolationthreshold for electrically conductive spheres (aspect ratio of one) isgreater than the percolation threshold for fibers. Accordingly, a higherconcentration of electrically conductive spheres is needed to achieve anelectrically conductive composite than would be required forelectrically conductive fibers.

[0120] The scaling relationship (i.e., power law) for electricalconductivity of a particulate loaded matrix is expressed as σ ∝(x−x_(c))^(t), where σ is the electrical conductivity, x is theconcentration (volume percent) of electromagnetically responsiveparticulate, x_(c) is the percolation threshold (x_(c) is dependent onthe geometry of the particle), and t is a corresponding criticalexponent. Typically, t is about 2.0.

[0121] Under conventional percolation theory, when the concentration ofthe electromagnetically responsive particulate reaches the percolationthreshold, the electrical conductivity of the composite risesprecipitously. This scaling law applies to the application of bothdirect current (DC) and alternating current (AC).

[0122] It should be appreciated that most composites have a non-zeroelectrical conductivity at concentrations of electromagneticallyresponsive particulate below the percolation threshold. It is believedthat this results from a percolation cluster that consists of thenearest-neighbors sub-network of the full tunneling network. While theconcentration of electromagnetically responsive particulate ispreferably selected to be equal or greater than the percolationthreshold, the concentration may also be selected to be less than thepercolation threshold, as long as a non-zero electrical conductivity isobtained.

[0123] It is believed that the conduction mechanism of the composite isnot by actual particle to particle contact. In this regard, there is athin layer of electrically non-conductive material between some of theelectromagnetically responsive particles. Accordingly, the electrons(which are the charge carriers in the composite) must quantummechanically tunnel from one particle to another through an interveninglayer of electromagnetically responsive material. Accordingly, theelectrical conductivity of the composite may not be as good as theelectrical conductivity of the electromagnetically responsive materialalone, i.e., the material from which the particles are made.

[0124] It should be understood that the dimensionality of theelectromagnetically responsive network may have a “fractal” (i.e., has adimensionality of between two and three) value. In other words, anetwork of electromagnetically responsive particles within anelectrically non-conductive material may have a dimensionality ofsomewhere between two and three, where a dimensionality of two is thedimensionality of a square, and a dimensionality of three is thedimensionality of a cube.

[0125] It is further believed that a polymer with electromagneticallyresponsive particles embedded therein may also act as a current limitingpolymer to self-limit heat build-up, and thereby prevent melting of thepolymer. In this respect, a sufficient quantity of electromagneticallyresponsive particulates are blended within a polymer matrix such thatwhen desired operational parameters are obtained, the vaporizer operatesas a current limiting polymer. In other words, as the temperature of thevaporizer increases beyond the operating temperature, the polymer matrixheats and expands to the point where the electromagnetically responsiveparticles lose sufficient “contact” such that the electricalconductivity of the composite material decreases, thus limiting thecurrent flowing through the composite material, and thereby limiting thejoule heat produced. In this instance, the polymer matrix begins to cooluntil the polymer matrix contracts sufficiently for particle to particlecontact to be restored, in which case the vaporizer becomes operationalagain.

[0126] As indicated above, an AC source 50 supplies an alternatingcurrent to a coil 36. Electromagnetic radiation causes electrons to movein the electromagnetically responsive material, thereby resulting in theproduction of heat. Electromagnetically responsive materials couple toeither an electric field or an oscillating magnetic field to produce theheat. In the case of coupling to an electric field, the heat produced isjoule heat or I²R heat. In the case of coupling to an oscillatingmagnetic field, heat is produced through the generation of eddy currentsin the electromagnetically responsive material. It should be appreciatedthat, depending on the electromagnetically responsive particles used, amicrowave or RF generator that directs radiation toward theelectromagnetically responsive material may be substituted for coil 36.

[0127] It should be appreciated that the frequency of the alternatingcurrent can be varied, thereby causing the applied electromagneticradiation to penetrate heating tube 30 and/or insert 180 at variousdepths, as a result of “skin effect.” Skin effect will now be describedby way of the following example, where the vaporizer is comprised of aheating tube 30 and an insert 180. Heating tube 30 and/or insert 180 mayinclude electromagnetically responsive material.

EXAMPLE 1

[0128] heating tube: geometry: cylindrical

[0129] wall thickness=5 mm

[0130] material: resin bonded graphite

[0131] (skin depth)(square root of frequency)=δ{square root}{square rootover (f)}=1.592

[0132] where δ is the skin depth, and f is the frequency of theelectromagnetic radiation applied to the heating tube of Example 1. At afrequency of f=101.4 kHz, the applied electromagnetic radiation willhave decreased to 1/e its initial value within the wall thickness oftube 30 (i.e., 5 mm). To energize electromagnetically responsivematerial in the insert, electromagnetic radiation of a frequency (f₁)less than 101.4 kHz should be used. In this regard, a frequency (f₁)less than 101.4 kHz will result in a skin depth greater than the 5 mmwall thickness of tube 30. Accordingly, the emitted radiation has awavelength that allows propagation through tube 30, and will impingedirectly on electromagnetically responsive material in insert 180. Thus,insert 180 is heated directly by induction, rather than by conduction.It should be understood that the frequency of the electromagneticradiation may be varied such that only tube 30 is exposed toelectromagnetic radiation at a first frequency, and tube 30 and insert180 are exposed to electromagnetic radiation at a second frequency.Accordingly, the frequency of the electromagnetic radiation can bevaried to alternately heat (1) tube 30 and (2) tube 30 and insert 180.

[0133] Referring now to FIG. 10, there is shown a vaporizer 12 having atube 230 comprised of an electrically non-conductive material 231embedded with electromagnetically responsive particles 240. In theillustrated embodiment, electrically non-conductive material 231 is apolymer, and electromagnetically responsive particles 240 are metalfibers. Tube 230 includes an inner surface 232 and an outer surface 234.Inner surface 232 defines a bore 236.

[0134]FIGS. 11-14 illustrate tube 230, wherein alternative particletypes are used for electromagnetically responsive particles 240. In thisregard, FIG. 11 shows electromagnetically responsive particles 240 inthe form of granular metal particles, embedded in electricallynon-conductive material 231.

[0135]FIG. 12 shows a heating tube 230 comprised of electromagneticallyresponsive particles 240 in the form of metal flakes, embedded inelectrically non-conductive material 231.

[0136]FIG. 13 shows a heating tube 230 comprised of electromagneticallyresponsive particles 240 in the form of metal coated spheres, embeddedin electrically non-conductive material 231. The metal coated spheresare generally comprised of a glass spheres 252 coated with a metalcoating 254, as best seen in FIG. 14. As discussed above, glass spheres252 may be coated with an electromagnetically responsive materialautocatalytically or by electrodeposition.

[0137] Referring now to FIG. 15, there is shown a heating tube 230comprised of an electrically non-conductive material 231 embedded withelectromagnetically responsive particles 240, and a layer 260 ofelectromagnetically responsive material. Layer 260 ofelectromagnetically responsive material is formed on inner surface 232of tube 230. Layer 260 may be formed by conventionally known depositiontechniques (discussed below), or may be a preformed component. In theillustrated embodiment, electromagnetically responsive particles 240 aremetal fibers.

[0138] Referring now to FIG. 16 there is shown a heating tube 230comprised of an electrically non-conductive material 231 embedded withelectromagnetically responsive particles 240, and a layer 270 ofelectrically non-conductive material on inner surface 232 of tube 230.In this embodiment of the present invention, layer 270 of electricallynon-conductive material (e.g., a polymer) isolates antimicrobial fluidsfrom electromagnetically responsive particles 240. In this regard, onlylayer 270 of electrically non-conductive material is exposed to theantimicrobial fluids. By way of example, and not limitation, layer 270of electrically non-conductive material may be applied to inner surface232 by conventionally known deposition techniques. Alternatively, layer270 of electrically non-conductive material may be preformed (e.g., bymolding).

[0139]FIG. 17 illustrates a tube 309 including a tube wall 32 comprisedof an electromagnetically responsive material, such as iron, zinc,carbon steel, stainless steel, aluminum, copper, brass, or bronze, asdiscussed above in connection with tube 30. A layer 270 of electricallynon-conductive material lines inner surface 52 of tube wall 32. In thismanner, layer 270 of electrically non-conductive material isolates theelectromagnetically responsive material from antimicrobial fluids.Accordingly, only layer 270 of electrically non-conductive material isexposed to antimicrobial fluids. By way of example, and not limitation,layer 270 of electrically non-conductive material may be coated ontoinner surface 232 by conventionally known deposition techniques.Alternatively layer 270 of electrically non-conductive material may bepreformed (e.g., by molding).

[0140]FIG. 18 illustrates an embodiment of the present invention,wherein microwave energy is generated to produce heat. Tube 230 ispreferably comprised of electrically non-conductive material 231 havingelectromagnetically responsive particles 240 embedded therein. Theelectromagnetically responsive material 231 is preferably a materialthat produces heat as the material is driven through its electric ormagnetic hysteresis loop.

[0141] A microwave generator 250 provides a source of electromagneticenergy. Microwave generator 250 may take the form of a magnetron thatgenerates electromagnetic energy. Microwave generator 250 generatesmicrowaves, i.e., electromagnetic radiation having a frequency of about1 GHz to about 300 GHz. In one embodiment, glass containing ferriteparticles is exposed to microwaves. It is believed that the changingmagnetic field of the microwaves drives the ferrite particles throughtheir magnetic hysteresis loops, thus magnetically working theparticulates. This magnetic working results in the ferrite particlesheating up. The heat is transferred to the glass (e.g., Pyrex®) matrix.In a similar manner, ferroelectric particulate can be mixed within apolymer, a ceramic or glass matrix. In this case, it is believed thatthe oscillating electric field of an incident electromagnetic wavedrives the particles through their electric hysteresis loops generatingheat.

[0142] Electromagnetically responsive material 231 may be selected fromthe group, including, but not limited to: a ferromagnetic (iron) and/ora ferrimagnetic material (ferrites, e.g., magnetite (Fe₃O₄) orFeO.Fe₂O₃), or a ferroelectric (such as perovskites, e.g., lead titanate(PbTiO₃)) and/or a ferrielectric material. One specific exemplarymaterial is metalized polyethylene terephthalate (PET), commonly used inmicrowavable food packages to speed the cooking process.

[0143] As an alternative to the embodiment illustrated in FIG. 18, tube230 may be comprised of an electrically non-conductive material 231, butwithout any embedded electromagnetically responsive particles. A layerof electromagnetically responsive material 240 (e.g., a metalizedpolymeric film, such as metalized PET) coats inner surface 232 of tube230.

[0144] As indicated above, the electromagnetically responsive materialmay be in the form of a layer of material on a surface of heating tube30 and/or insert 180 (e.g., see FIG. 15). The electricallynon-conductive material may alternatively be in the form of a protectivecoating layer on a surface of heating tube 30 and/or insert 180 (e.g.,see FIGS. 16 and 17). Layers of electromagnetically responsive materialand electrically non-conductive material may be formed by conventionallyknown deposition techniques, including, but not limited toelectrodeposition, autocatalytic deposition, arc spraying, and thermalspraying.

[0145] According to the further contemplated embodiments of the presentinvention, the heating tube and/or insert may be produced by a varietyof techniques, including, but not limited to conventional molding,injection molding, or extrusion. Extrusion or injection molding arepreferred for a thermoplastic polymer. Conventional molding is preferredin the case of a thermosetting polymer. In the case of an extruded tubeor insert, electromagnetically responsive particulate can be added to anextruder along with a polymer to produce a cylinder of a compositematerial.

[0146]FIGS. 19 and 20 illustrate a heating tube 330 having multiplebores 336 formed therein to provide multiple pathways. Tube 330 iscomprised of electromagnetically responsive particles 240 embedded in anelectrically non-conductive material 231. Heating tube 330 may beproduced by conventionally known means, including, but not limited tomolding, injection molding, extrusion and spin casting. Bores 336 may beformed therein by drilling.

[0147]FIGS. 21 and 22 illustrate yet another embodiment of the heatingtube. Tube 430 is comprised of electromagnetically responsive particles240 embedded in an electrically non-conductive material 231. Tube 430 isformed of two half-cylinder portions 430 a, 430 b with grooves 432machined therein. Grooves 432 include a single groove portion 432 a anda multi-groove portion 432 b. Heating tube 430 may be produced bymolding, injection molding, or extrusion. The two half-cylinder portions430 a, 430 b may be joined ultrasonically or otherwise (FIG. 22) to forma cylinder with veins that act as flow paths. Atomized antimicrobialfluids can be dispersed into the veins. It should be appreciated thatadditional flow paths may be formed by machining.

[0148]FIGS. 23 and 24 illustrate tube 230 comprised ofelectromagnetically responsive particles 240 embedded in an electricallynon-conductive material 231. A screw-shaped insert 280 is comprised ofelectromagnetically responsive particles 240 embedded in an electricallynon-conductive material 231. A spiral passageway 282 is defined byscrew-shaped insert 280. Atomized antimicrobial fluids can be dispersedinto spiral passageway 282. As shown in FIG. 24, insert 280 is locatedinside tube 230.

[0149] The heating tube and/or insert may have geometric shapes otherthan those illustrated herein. Furthermore, use of an electricallynon-conductive material that can be molded or extruded (e.g., a polymer)facilitates production of heating tubes and inserts of a wide variety ofgeometric shapes. This also allows the heating tube and insert to beconveniently formed as an integrated component. It should also beappreciated that one or more elbows may be attached to a cylindricalheating tube and/or insert, wherein the elbow provides a “wall” uponwhich an atomized antimicrobial fluid can impinge and thus vaporize.

[0150] It should be understood that the present invention may alsoinclude a temperature sensing device to prevent overheating of thevaporizer that could result in melting or destruction of anyelectrically non-conductive material. One exemplary temperature sensingdevice is a thermocouple that senses temperature changes by using a pairof joined wires made of dissimilar metals that produces a voltage thatchanges with temperature.

[0151] Use of an electrically non-conductive material as described abovemay provide several advantageous effects. In this regard, the vaporizerweight and manufacturing costs can be reduced. Furthermore, electricallynon-conductive material can be used to insulate electromagneticallyresponsive material from antimicrobial fluids. Accordingly,antimicrobial fluids such as water, hydrogen peroxide, peracids, and thelike can be used without concern about degradation to the antimicrobialfluids by the electromagnetically responsive material (e.g., copper).

[0152] The invention has been described with reference to preferredembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations insofar as they come within thescope of the appended claims or the equivalents thereof. Othermodifications and alterations will occur to others upon their readingand understanding of the specification. It is intended that all suchmodifications and alterations be included insofar as they come withinthe scope of the invention as claimed or the equivalents thereof.

Having described the invention, the following is claimed:
 1. A vaporizerfor vaporizing a fluid to form an antimicrobial vapor, comprising: asource of electromagnetic radiation; and a heating apparatus forproducing heat to vaporize an antimicrobial fluid passing therethrough,including: (a) an electrically non-conductive material, and (b) anelectromagnetically responsive material.
 2. A vaporizer as defined byclaim 1, wherein said electrically non-conductive material is selectedfrom the group consisting of: a polymer, a ceramic and a glass.
 3. Avaporizer as defined by claim 2, wherein said polymer is selected fromthe group consisting of: a thermoplastic polymer and a thermosettingpolymer.
 4. A vaporizer as defined by claim 3, wherein saidthermoplastic polymer is selected from the group consisting of: a nylon;Amodel® (PPI, polyphthalamide); Aurum® (polyimide); Ryton®/Fortron®(PPS, polyphenylenesulphide); Fluoropolymers (PFA, FEP, Tefzel® ETFE,Halar® ECTFE, Kynar® PVDF); Teflon® PTFE; Stanyl® (4.6 polyamide, 4.6Nylon); Torlon® (polyamide-imide); Ultem® (polyetherimide, PEI); andVictrex® PEEK (polyaryletherketone, polyetheretherketone).
 5. Avaporizer as defined by claim 3, wherein said thermosetting polymer isselected from the group consisting of: an epoxy and a urethane.
 6. Avaporizer a defined by claim 2, wherein said ceramic is a metal-oxidematerial.
 7. A vaporizer as defined by claim 6, wherein said ceramic isselected from the group consisting of: silica, alumina, and magnesia. 8.A vaporizer as defined in claim 1, wherein said electromagneticallyresponsive material is selected from the group consisting of: a metal, ametal alloy, a metal coated material, carbon, graphite, stainless steel,a metal alloy solder, a ferromagnetic material, a ferrimagneticmaterial, a ferroelectric material, a ferrielectric material, andcombinations thereof.
 9. A vaporizer as defined in claim 8, wherein saidmetal is selected from the group consisting of: nickel, copper, zinc,silver, stainless steel, tungsten, nichrome, and combinations thereof.10. A vaporizer as defined in claim 1, wherein said electromagneticallyresponsive material is a ferromagnetic material.
 11. A vaporizer asdefined in claim 1, wherein said electromagnetically responsive materialis a ferrimagnetic material.
 12. A vaporizer as defined in claim 1,wherein said electromagnetically responsive material is a ferroelectricmaterial.
 13. A vaporizer as defined in claim 1, wherein saidelectrically non-conductive material forms an electricallynon-conductive matrix, said electromagnetically responsive material isembedded within the electrically non-conductive matrix.
 14. A vaporizeras defined by claim 13, wherein said electromagnetically responsivematerial is in the form of a particulate selected from the groupconsisting of: fibers, flakes, spheres, whiskers, grains, a coatedparticulate and combinations thereof.
 15. A vaporizer as defined inclaim 1, wherein said electromagnetically responsive material forms alayer on a surface of said electrically non-conductive material.
 16. Avaporizer as defined in claim 15, wherein electromagnetically responsivematerial is embedded in said electrically non-conductive material.
 17. Avaporizer as defined in claim 15, wherein said electromagneticallyresponsive material is deposited on said electrically non-conductivematerial by at least one of: thermal spraying, electrodeposition,autocatalytic deposition, and arc spraying.
 18. A vaporizer as definedin claim 1, wherein said electrically non-conductive material forms alayer to provide a protective coating, said protective coating isolatingsaid electromagnetically responsive material from an antimicrobialfluid.
 19. A vaporizer as defined in claim 18, wherein saidelectromagnetically responsive material is embedded in an electricallynon-conductive material.
 20. A vaporizer as defined in claim 18, whereinsaid electromagnetically responsive material is deposited to form saidlayer by at least one of: thermal spraying, electrodeposition,autocatalytic deposition, and arc spraying.
 21. A vaporizer as definedin claim 1, wherein said source of electromagnetic radiation is amicrowave generator, said microwave generator generating microwaves thatcause heating of said electromagnetically responsive material.
 22. Avaporizer as defined in claim 21, wherein said electromagneticallyresponsive material is selected from the group consisting of: aferromagnetic material, a ferrimagnetic material, a ferroelectricmaterial and a ferrielectric material.
 23. A vaporizer as defined inclaim 1, wherein said source of electromagnetic radiation produces analternating current.
 24. A vaporizer as defined in claim 23, whereinsaid alternating current has at least a first frequency and a secondfrequency, wherein said electromnagnetic radiation penetrates saidheating apparatus at respective first and second depths.
 25. A vaporizeraccording to claim 1, wherein said heating apparatus includes: agenerally cylindrical tube, and a screw-shaped insert dimensioned to bereceived within said generally cylindrical tube, said screw-shapedinsert including a spiral passageway, wherein at least one of saidgenerally cylindrical tube and said screw-shaped insert are comprised ofsaid electrically non-conductive material and said electromagneticallyresponsive material.